1. Field of the Invention
The present invention relates to a removable protective casing for the protection of heavy and possibly hazardous articles during storage and/or transit. The protective casing is suitable for the protection of heavy cylinders containing gaseous substances and particularly, though not exclusively, for the protection of cylinders of uranium hexafluoride in transit.
2. Discussion of Prior Art
Gaseous uranium hexafluoride is the primary material from which nuclear fuels are made and is transported around the world in pressurised cylinders which are currently protected by a so-called xe2x80x9coverpackxe2x80x9d. The present protective overpack comprises stainless steel inner and outer skins having a filling of a phenolic resin or polyurethane foam in the intervening space between the skins. Due to the hazardous nature of the material being transported, the overpacks have to withstand rigorous tests set by regulatory bodies to ensure integrity if they are dropped from a height during handling for example and have also to provide a heat barrier and watertight protection for the contained cylinder. A 30xe2x80x3 diameter cylinder full of uranium hexafluoride and having the overpack described above may weigh up to 4000 kg. The overpack and cylinder must survive being dropped from 9m without damage to the cylinder. However, in some recent tests, deformation of the cylinder skirt and consequent damage to the cylinder valve through which the uranium hexafluoride is filled and removed has occurred. This has necessitated a complex, costly and difficult to fit valve protection member being added to the existing overpacks. The problems are exacerbated by corrosion of the overpack metal skins which allows the interior foam to become saturated with water making the overpacks even heavier and the absorbed water further increasing the corrosion rate in addition to that caused by the phenolic resin itself as the packs have to stay outside under virtually all climatic conditions. To further strengthen the present overpack, more metal components have been added which degrades the fire resistance due to increased thermal conductivity.
It is an object of the present invention to provide a protective casing which is lighter in weight, more durable and more easily repaired than the presently known overpack. It is a further object to provide a protective casing where no additional components to protect the valve of a contained cylinder are required. It is a yet further object to provide a protective casing having improved resistance to corrosion and weathering. It is a still further object to provide a protective casing having improved fire resistance.
According to the present invention there is provided a casing for the protection of an article contained within the casing, the protective casing comprising: at least two casing members which are assemblable to constitute a casing having an internal volume to receive the article, each of said at least two casing members comprising; an outer skin of fiber reinforced plastics material having a plurality of layers of reinforcing fibers in a plastics material matrix; an inner skin of fiber reinforced plastics material having a plurality of layers of reinforcing fibers in a plastics material matrix; a filling of a low density core material in a space between the outer and inner skin members; sealing means disposed in the joint face between said at least two casing members; and fastener means to hold said at least two members together.
The filling of low density core material is to provide an increase in the section modulus and to provide a crush zone in the event of impact.
Preferably, there are two casing members of generally semi-cylindrical form and the assembled casing may be of generally cylindrical form.
The casing members may not necessarily be of identical shape or construction.
Preferably, the outer casing skin comprises a plurality of layers of non-woven glass cloth and optionally aramid fiber layers having a matrix of a urethane acrylate, vinyl ester resin and/or polyester resin for example.
Preferably, the inner casing skin comprises a plurality of layers of non-woven glass cloth layers having a matrix of a polyester resin for example or the resin used in the outer casing skin.
However, other resin matrices such as epoxy or phenolic may be used in some applications.
The non-woven cloths may be 0xc2x0/90xc2x0 or 45xc2x0/45xc2x0 or may be a mixture of both for example.
Woven cloths, continuous filament or chopped-strand mat may also be used in some applications.
The different fiber layers may be arranged alternately or in groups of two for example.
The inner and outer skins may each have an overall thickness in the range from about 2 mm to about 25 mm.
The outer skin may also incorporate external ribbing to increase strength and stiffness of the casing members. The recesses in the external ribbing may also provide convenient protection for fasteners used to lock the casing members together.
The low density core material between the inner and outer skins may be a PVC or polyurethane foam material or timber-based such as cork or balsa wood for example. In the case of foam, the core may have fillers such as glass spheres for example to reduce the density of the foam.
A foam core in the region of the joint faces between the casing members may be a high density syntactic foam for example to increase the strength in this region.
Alternatively, another material such as wood may be used in this region if necessary.
The foam may itself be reinforced with various fillers such as clay, glass or ceramics for example. Glass fillers may also incorporate neutron or radiation shielding materials.
The foam may be introduced in the form of a liquid and foamed in-situ or may be in sheet form, curved by the application of heat and bonded to the facing surfaces of the inner and outer skins by an adhesive. Alternatively, the foam core may be cut from block material.
The thickness of the foam core may lie in the range from about 10 mm to about 200 mm.
The inner surface of the outer skin may have reinforcements bonded or otherwise incorporated to allow for the attachment of components by bolting, for example, to the outside of the casing. Such reinforcements may comprise materials such as wood or metals such as steel for example. Such components may include cradle members to allow for the convenient stacking and handling of the casing and contained cylinders during transportation and storage.
Corners of the protective casing may also further include reinforcing members such as additional layers of fibers and resin and/or embedded metal members. However, in order to maximise the fire resistance of the casing according to the present invention, the inclusion of metal members is desirably reduced to a minimum.
The faces of the casing members which constitute the joints therebetween may be provided with seal members to prevent ingress of water.
The joint faces may also be provided with intumescent seals which expand when subjected to heat to further protect the enclosed article.
The outside of the casing in the joint region for example may be provided with an additional protective layer comprising, for example, a coating of a rubber to further improve abrasion and impact resistance.
It has been found that the strength of the protective casing according to the present invention is sufficient to meet all the test procedures for cylinders of uranium hexafluoride for example at a significantly lighter overall weight than the presently used overpacks.
The method of manufacture may be by resin transfer moulding or resin infusion. Resin infusion and resin transfer (RTM) are processes where resin is injected into a fiber filled cavity between two mould surfaces.
Alternatively, the method of manufacture of protective casings according to the present invention may be by conventional laying up of layers of reinforcing fibers sequentially in a mould and impregnating with the appropriate resin followed by curing for example.
Casings of the present invention may be easily repaired unlike known overpacks for example.